Multiple Description Coding (MDC) is known in the art to be an effective technique for robust communication over networks, such as wireless networks that are subjected to multi-path interference and Doppler diversity. MDC is also employed in transmission of data distributed over a plurality of disk drives, e.g., Redundant Arrays of Inexpensive Disks (RAIDS), and the Internet. Several types of MDC coding schemes are known. For example, Servetto, et al., teach scalar quantization, in “Multiple Description Lattice Vector Quantization,” Proceedings of the IEE Data Compression Convergence (DCC), Snowbird, Utah., March 1999. Y. Wang, et al., teach correlating transforms in “Multiple Description Coding using Pairwise Correlating Transforms,” January 1999. Goyal, Vetteri, et al., teach frame expansion in “Multiple Description Transform Coding: Robustness to Erasures Using Tight Frame Expansion,” August 1998. Puri et al., teach Forward Error Correction (FEC) in “Forward Error Correction (FED) Codes Based on Multiple Description Coding for Internet Video Streaming and Multicast Signal Processing,” Image Communication, Vol. 16, No. 8, pp. 745-762, May 2001.
FIG. 1 illustrates an MDC method 100 proposed by J. G. Apostolopoulos in “Reliable Video Communication Over Lossy Packet Networks using Multiple State Encoding and Path Diversity,” Visual Communications and Image Processing (VCIP), pp. 392-409, January 2001, wherein video data composed of a plurality of image frames, represented as 110a, 110b, 110c, are split into odd frames, represented as 121, 123, 125, of information and even frames, represented as 122, 124, 126, of information. The video information in each odd and even frame is then independently coded using known encoding techniques, such as MPEG, etc. The coded information in each odd and even frame may then be transmitted over a network using the same or different channels. In this latter case, the time to transmit an entire image may be significantly reduced. As would be appreciated, the information referred to as “odd” and “even” may, for example, be information associated with “odd” and “even” rows of video data in a video image.
In the current state-of-the-art, MDC encoding algorithms assume that at least one channel is operating at a maximum bit-rate or bandwidth. However, this assumption does not consider that the network bandwidth varies over time and could fall below a level suitable for MDC coded images. In such a case, the transmitted images are not properly decoded and the image quality at the receiver may be sufficiently degraded to render the image un-viewable.
Accordingly, there is a need for a method of MDC coding that is responsive to the varying amount of available network bandwidth and can dynamically adjust the transmission rate to accommodate available network bandwidth.